Back to EveryPatent.com
United States Patent |
5,115,768
|
Peschka
,   et al.
|
May 26, 1992
|
Combustion engine for hydrogen
Abstract
In order to improve a combustion engine for hydrogen comprising a main
piston which is displaceable in a main cylinder in a stroke direction
between a top dead center, forming a minimum main cylinder chamber with
the main cylinder, and a bottom dead center and hereby performs a suction
stroke, a compression stroke, a displacement stroke and an exhaust stroke,
such that the problems of early ignition are avoided without any internal
mixture formation with late injection being required, it is recommended
that an auxiliary piston and an auxiliary cylinder be provided for
movement relative to one another so as to be in equal phase and
synchronous with the main piston and the main cylinder, that the auxiliary
piston and the auxiliary cylinder define with one another a cylinder
chamber varying between a minimum cylinder chamber in the top dead center
and a maximum cylinder chamber in the bottom dead center, that the minimum
cylinder chamber communicate with the minimum main cylinder chamber via a
passage and that the hydrogen be injected into the cylinder chamber during
the course of the suction stroke.
Inventors:
|
Peschka; Walter (Sindelfingen, DE);
Schneider; Gottfried (Stuttgart, DE)
|
Assignee:
|
Deutsche Forschungsanstalt fur Luft- und Raumfahrt e.V. (DE)
|
Appl. No.:
|
652325 |
Filed:
|
February 7, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
123/1A; 123/58.6; 123/289; 123/DIG.12 |
Intern'l Class: |
F02B 075/12 |
Field of Search: |
123/1 A,269,289,59 BS,73 F,65 S,304,527,DIG. 12
|
References Cited
U.S. Patent Documents
4069794 | Jan., 1978 | Jordan | 123/59.
|
4367698 | Jan., 1983 | Skala | 123/1.
|
4478180 | Oct., 1984 | Fujikawa et al. | 123/59.
|
4485779 | Dec., 1984 | Spurk | 123/289.
|
4508064 | Apr., 1985 | Watanabe | 123/DIG.
|
Foreign Patent Documents |
568918 | Jan., 1933 | DE2.
| |
724065 | Jul., 1942 | DE2.
| |
851701 | Oct., 1952 | DE.
| |
2517066 | Oct., 1976 | DE | 123/DIG.
|
2525547 | Dec., 1976 | DE | 123/DIG.
|
Other References
Patent Abstracts of Japan, No. 54-52203, vol. 3, No. 76 (M-64), Jun. 29,
1979.
Patent Abstracts of Japan, No. 57-83626, vol. 6, No. 172 (M-154), Sep. 7,
1982.
|
Primary Examiner: Okonsky; David A.
Attorney, Agent or Firm: Lipsitz; Barry R.
Claims
What is claimed is:
1. Combustion engine for hydrogen comprising a main piston displaceable in
a main cylinder in a stroke direction between a top dead center, forming a
minimum main cylinder chamber with the main cylinder, and a bottom dead
center and hereby performing a suction stroke, a compression stroke, a
displacement stroke and an exhaust stroke, characterized in that an
auxiliary piston (44) and an auxiliary cylinder (42) are provided for
movement relative to one another so as to be in equal phase and
synchronous with the main piston (12) and the main cylinder (10), that the
auxiliary piston (44) and the auxiliary cylinder (42) define with one
another a cylinder chamber (66) varying between a minimum cylinder chamber
(66a) in the top dead center and a maximum cylinder chamber (66b) in the
bottom dead center, that the minimum cylinder chamber (66a) communicates
with the minimum main cylinder chamber (36a) via a passage (68) and that
the hydrogen is injected into the cylinder chamber (66) during the course
of the suction stroke.
2. Combustion engine as defined in claim 1, characterized in that the
passage is at least partially formed by a gap (68) between the auxiliary
piston (44) and the auxiliary cylinder (42).
3. Combustion engine as defined in claim 2, characterized in that the
smallest radial width of the gap (68) between the auxiliary piston (44)
and the auxiliary cylinder (42) varies between the top dead center and the
bottom dead center.
4. Combustion engine as defined in claim 1, characterized in that the
auxiliary piston (44) and the auxiliary cylinder (42) move relative to one
another in the stroke direction (14) of the main piston (12).
5. Combustion engine as defined in claim 1, characterized in that the
auxiliary piston (44) and the auxiliary cylinder (42) travel, relative to
one another, along the same path as the main piston (12).
6. Combustion engine as defined in claim 1, characterized in that the
displaceable auxiliary piston (44) or auxiliary cylinder (42),
respectively, is coupled to the main piston (12) via a connecting member
(48).
7. Combustion engine as defined in claim 6, characterized in that the
stationary auxiliary cylinder (42) or auxiliary piston (44) is rigidly
connected to the main cylinder (10) and that the displaceable auxiliary
piston (44) or auxiliary cylinder (42), respectively, is held on the main
piston (12).
8. Combustion engine as defined in claim 7, characterized in that the
auxiliary piston (44) or auxiliary cylinder (42) is held on the main
piston (12) with clearance transverse to the stroke direction (14).
9. Combustion engine as defined in claim 7, characterized in that the
auxiliary piston (44) rises above a base (46) of the main piston (12).
10. Combustion engine as defined in claim 1, characterized in that the
auxiliary cylinder (42) extends away from the minimum cylinder chamber
(36a).
11. Combustion engine as defined in claim 10, characterized in that the
auxiliary cylinder (42) extends in the stroke direction (14) of the main
piston (12).
12. Combustion engine as defined in claim 10, characterized in that the
auxiliary cylinder (42) forms an extension of the main cylinder (10).
13. Combustion engine as defined in claim 1, characterized in that the
combustion engine is provided with a main injection means (72) opening
into the main cylinder chamber (36) and generating a weak mixture during
the suction stroke, and that for enriching the mixture an enriching
injection means (64) into the cylinder chamber (66) is provided.
Description
The invention relates to a combustion engine for hydrogen comprising a main
piston displaceable in a main cylinder in a stroke direction between a top
dead center, forming a minimum main cylinder chamber with the main
cylinder, and a bottom dead center and hereby performing a suction stroke,
a compression stroke, a displacement stroke and an exhaust stroke.
Combustion engines for hydrogen of this type are known. These can be
operated in a number of different ways. A first possibility is the
external mixture formation with hydrogen with which the hydrogen/air
mixture is produced outside the cylinder chamber and this is then drawn in
as in a normal internal combustion engine for fossil fuels.
Another possibility is the internal mixture formation which provides for
injection of the hydrogen directly into the main cylinder chamber, a
difference being made between an early injection, i.e. at the beginning of
the compression stroke, and a late injection, i.e. injection substantially
near to the end of the compression stroke.
In contrast to internal combustion engines for fossil fuels, in the case of
combustion engines for hydrogen power losses result both with the external
mixture formation with hydrogen and with the internal mixture formation
with early injection in the range of full load due to uncontrolled early
ignition since the hydrogen/air mixture is heated at hot parts of the
engine and therefore ignites prematurely.
This uncontrolled early ignition can be avoided when using internal mixture
formation with late injection of hydrogen since the ignitable hydrogen/air
mixture does not result until towards the end of the compression stroke.
However, the internal mixture formation with late injection does have the
disadvantage that is it very difficult to homogenize the mixture
sufficiently for combustion and so local inhomogeneities constantly result
and these lead to a high emission of nitrogen oxide. In addition, problems
also occur, at the customary speeds of internal combustion engines, when
trying to inject, distribute and ignite the required volume of hydrogen in
the combustion chamber during the short time available. This requires, for
example, in the initial load range .injection pressures in the order of
100 to 200 bars in view of the greater volume of hydrogen in comparison
with fossil fuels having the same energy content.
The object underlying the invention is therefore to improve a combustion
engine for hydrogen such that the problems of early ignition are avoided
without any internal mixture formation with late injection being
necessary.
This object is accomplished in accordance with the invention, for a
combustion engine of the type described at the outset, in that an
auxiliary piston and an auxiliary cylinder are provided for movement
relative to one another so as to be in equal phase and synchronous with
the main piston and the main cylinder, that the auxiliary piston and the
auxiliary cylinder define with one another a cylinder chamber varying
between a minimum cylinder chamber in the top dead center and a maximum
cylinder chamber in the bottom dead center, that the minimum cylinder
chamber communicates with the minimum main cylinder chamber via a passage
and that the hydrogen is injected into the cylinder chamber during the
course of the suction stroke.
The inventive solution has the advantage that due to injection of the
hydrogen into the cylinder chamber during the suction stroke a relatively
low pressure is first required for this injection and a relatively long
time is available. In addition, the hydrogen is compressed in the cylinder
chamber during the compression stroke and flows during this compression
stroke through the passage into the main cylinder chamber, leading to
turbulences in the main cylinder chamber due to flow through the passage
and these turbulences ensure that the hydrogen is mixed well with the air.
Furthermore, at the beginning of the compression stroke the hydrogen/air
mixture in the main cylinder chamber is not yet ignitable and does not
become ignitable until immediately prior to the top dead center being
reached since it is not until this time that the hydrogen is more or less
completely expelled from the cylinder chamber into the main cylinder
chamber.
In this way, the inventive solution combines the advantages of the internal
mixture formation with early injection, relating to the time available for
injecting the hydrogen and the low pressures required, and the advantages
of the internal mixture formation with late injection with a view to the
fact that early ignition is avoided since the mixture in the main cylinder
chamber does not become ignitable until more or less immediately prior to
the top dead center being reached.
According to the invention, the main cylinder chamber and the cylinder
chamber are separated in all stroke positions and connected via the
passage.
Theoretically, the auxiliary cylinder and the auxiliary piston can be
arranged independently of the main piston and main cylinder and a transfer
passage provided between the two. It is, however, particularly
advantageous for the passage to be at least partially formed by a gap
between the auxiliary piston and the auxiliary cylinder. This means that
due to the relative movement of auxiliary piston and auxiliary cylinder
control of the transfer velocity from the cylinder chamber into the main
cylinder chamber is possible, in addition.
This control possibility can be achieved particularly easily in that the
smallest radial distance of the gap between the auxiliary piston and the
auxiliary cylinder varies between the top dead center and the bottom dead
center.
In the embodiments described thus far, the auxiliary cylinder and the
auxiliary piston can, as already mentioned, be arranged independently of
the main piston and main cylinder. It is, however, particularly
advantageous for the auxiliary piston and the auxiliary cylinder to be
displaced relative to one another in the stroke direction of the main
piston, i.e. both move in the same direction as the main piston.
From a constructional point of view, the inventive combustion engine can be
realized in a particularly simply manner by the auxiliary piston and the
auxiliary cylinder travelling, relative to one another, along the same
path as the main piston. Particularly in the latter case, the synchronous
coupling of the movement of the auxiliary piston relative to the auxiliary
cylinder with the main piston is achieved by coupling the displaceable
auxiliary piston or auxiliary cylinder, respectively, with the main piston
via a connecting member.
This connecting member can be of the most varied type and construction. For
example, it is possible to provide a coupling rod as connecting member.
In the simplest case, however, the stationary auxiliary cylinder or
auxiliary piston is rigidly connected to the main cylinder and the
displaceable auxiliary piston or auxiliary cylinder is held on the main
piston. In this case, the two movable parts are rigidly held on one
another so that synchronous movement thereof is possible in the simplest
manner.
In order to achieve compensation for play and, in particular, to ensure
that the gap between auxiliary cylinder and auxiliary piston can readjust
itself, the auxiliary piston or auxiliary cylinder, respectively, is held
on the main piston with clearance transverse to the stroke direction so
that the two movable parts can still, relative to one another, move
transversely to the stroke direction to provide such compensation for
play.
In the simplest case, the auxiliary piston extends beyond a base of the
main piston.
In addition, in this case the auxiliary cylinder extends away from the
minimum cylinder chamber.
Particularly when relative movement of the auxiliary cylinder and the
auxiliary piston is intended to be in the stroke direction, the auxiliary
cylinder extends in the stroke direction of the main piston and preferably
forms an extension of the main cylinder.
Particularly advantageous is, in addition, an embodiment of the inventive
combustion engine, in which this is provided with a main injection means
opening into the main cylinder chamber and generating a weak operation
during the suction stroke and in which for enriching the mixture an
enriching injection means is provided in the cylinder chamber.
This has the advantage that the basic enrichment of the hydrogen/air
mixture is carried out via the injection directly into the main cylinder
chamber and so auxiliary cylinder and auxiliary piston can be of a very
small construction as these merely have to perform an enriching injection
and so the inventive combustion engine is, altogether, of a very small
construction.
Additional features and advantages of the inventive solution are the
subject matter of the following description as well as of the drawings of
several embodiments. In these drawings:
FIG. 1 shows a first embodiment illustrated schematically in cross section;
FIG. 2 is an illustration similar to FIG. 1 of the first embodiment in the
top dead center;
FIG. 3 is an illustration similar to FIG. 1 of the first embodiment in the
bottom dead center and
FIG. 4 is an illustration similar to FIG. 1 of a second embodiment.
A first embodiment of an inventive combustion engine for hydrogen,
illustrated in FIG. 1, comprises a main cylinder 10 in which a main piston
12 is adapted for reciprocating movement in a stroke direction 14, between
a top dead center illustrated in FIG. 2 and a bottom dead center
illustrated in FIG. 3. The main piston 12 is connected by way of a piston
rod 16 to a crankshaft 18 which, itself, rotates about an axis 20 of a
driven shaft 22 of the combustion engine. An inlet passage 24 opens into
the main cylinder 10 in an inlet opening 26 which is adapted to be closed
by an inlet valve 28. In addition, an outlet passage 30 leads from the
main cylinder 10, starting from an outlet opening 32 which is also adapted
to be closed by an outlet valve 34.
A main cylinder chamber 36 is enclosed by the main piston 12 and the main
cylinder 10.
In its top dead center illustrated in FIG. 2, the main piston 12 with the
main cylinder 10 encloses a minimum main cylinder chamber 36a while the
main piston 12 in its bottom dead center illustrated in FIG. 3 encloses
with the main cylinder 10 a maximum main cylinder chamber 36b.
Ignition of a hydrogen/air mixture present in the main cylinder chamber 36
is carried out by an ignition element 38.
The main piston 12 is arranged coaxially to a cylinder axis 40 of the main
cylinder 10 and moves parallel thereto in the stroke direction 14.
An auxiliary cylinder 42 is linked with the main cylinder 10 and this is
arranged coaxially to the cylinder axis 40 and extends away from the main
piston 12. An auxiliary piston 44 is mounted for displacement in this
auxiliary cylinder 42 and this piston is also arranged coaxially to the
cylinder axis 40 and rises above a base 46 of the main piston 12 in the
direction of the auxiliary cylinder 42.
The auxiliary piston 44 is preferably held non-displaceably in the stroke
direction 14 on the main piston 12 with an auxiliary piston foot 48. This
auxiliary piston foot 48 comprises an annular flange 50 which is located
in a recess 52 arranged on the base side in the main piston 12 and is held
in this recess by a base cover 54 having an opening 56 and an edge region
58 surrounding the opening 56 which engages over the annular flange 50.
The opening 56, through which the auxiliary piston 44, proceeding from its
auxiliary piston foot 48, projects beyond the base 48 in the direction of
the auxiliary cylinder 42, and the recess 52 are preferably dimensioned
such that the auxiliary piston foot 48 has clearance in the radial
direction relative to the cylinder axis 40 and so can move to a slight
extent in the radial direction relative to the cylinder axis 40 in order
to constantly take up a central position relative to the auxiliary piston
44.
In the simplest case, the auxiliary piston 44 is completely cylindrical and
the auxiliary cylinder 42 is also designed to be cylindrical to the
cylinder axis 40 and extends from an auxiliary cylinder opening 60 in the
main cylinder 10 to an auxiliary cylinder head 62 which closes the
auxiliary cylinder 42. A hydrogen injector 64 is inserted into the
auxiliary cylinder head 62 and this injects hydrogen of, for example, 15
bars, into the auxiliary cylinder 42.
The auxiliary piston 44 forms with the auxiliary cylinder 42 a cylinder
chamber 66 which, in the top dead center of the main piston 12, is the
minimum cylinder chamber 66a and, in the bottom dead center of the main
piston 12, the maximum cylinder chamber 66b.
The cylinder chamber 66 communicates with the main cylinder chamber 36 via
a gap 68 formed between the auxiliary piston 44 and the auxiliary cylinder
42, i.e. its cylinder surfaces. This gap is intentionally large in design
and represents a transfer passage between the cylinder chamber 66 and the
main cylinder chamber 36.
The inventive combustion engine, illustrated in FIGS. 1 and 3, operates as
follows:
During a suction stroke the main piston 12 moves together with the
auxiliary piston 44 from the top dead center, illustrated in FIG. 2, to
the bottom dead center, illustrated in FIG. 3. In this case, the inlet
opening 26 is released by the inlet valve 28 so that air can flow into the
main cylinder chamber 36 through the inlet passage 24. At the same time,
hydrogen at a pressure of approximately 10 to 20 bars is injected into the
cylinder chamber 66 via the hydrogen injector 64. Since the gap 68 is very
small in dimension, only a very small amount of the hydrogen flows into
the main cylinder chamber 36 and so an extremely weak hydrogen/air mixture
is formed therein and this is not ignitable.
During a compression stroke the main piston 12 moves together with the
auxiliary piston 44 from the bottom dead center, illustrated in FIG. 3, to
the top dead center, illustrated in FIG. 2. The increasing compression in
the cylinder chamber 66 now results in an increasing amount of the
hydrogen flowing from the cylinder chamber 66 via the gap 68 into the main
cylinder chamber 36a and increasingly enriching the extremely weak
hydrogen/air mixture therein but leaving this so weak over broad regions
of the compression stroke that this is not ignitable and the hydrogen/air
mixture in the main cylinder chamber 36 is not enriched enough to be
ignitable until towards the end of the compression stroke. This means that
an ignitable mixture does not result in the main cylinder chamber 36 until
shortly before the top dead center is reached and so the mixture formation
is comparable with respect to its ignitability to the internal mixture
formation having late commencement of injection, i.e. commencement of
injection in the vicinity of the top dead center.
This avoids the problem of early ignition occurring in the internal mixture
formation with early injection.
Moreover, the displacement of the hydrogen out of the cylinder chamber 66
and the transfer thereof through the gap 68 into the main cylinder chamber
36 causes, in the main cylinder chamber, a very strong turbulence in the
hydrogen together with the compressed air and so, consequently, the
hydrogen/air mixture is very well mixed locally due to the resulting
turbulences.
During the subsequent combustion stroke the main piston 12 and the
auxiliary piston 44 non-displaceably connected therewith in the stroke
direction 14 move from the top dead center to the bottom dead center while
the main cylinder chamber 36 expands and during the subsequent exhaust
stroke the combusted hydrogen/air mixture is expelled through the outlet
opening 32, with the outlet valve 34 open, via the outlet passage 30.
Subsequently, this combustion engine commences a new cycle of operation.
In a second embodiment of the inventive combustion engine, illustrated in
FIG. 4, the auxiliary piston 44' is, in contrast to the auxiliary piston
44, not completely cylindrical in design but narrows in its central
portion 70 so that the width of the gap 68' formed between the auxiliary
cylinder 42 and the auxiliary piston 44' and, therefore, the width of the
transfer passage between the cylinder chamber 66 and the main cylinder
chamber 36 varies between the top and bottom dead centers according to the
position of the auxiliary piston 44'.
For example, the width of the gap 68' is large during a compression stroke,
starting from the bottom dead center, and so at the beginning of the
compression stroke a slighter volume of hydrogen is displaced out of the
auxiliary cylinder 44, although this can easily reach the main cylinder
chamber 36 due to the larger width of the gap 68', whereas once the
central region 70 has passed through the auxiliary cylinder opening 60 the
gap 68' is less wide and so the hydrogen from the cylinder chamber 66 can
no longer flow so easily into the main cylinder chamber 36. This means,
for example, that at the beginning of the compression stroke the hydrogen
can easily be transferred into the main cylinder chamber 36, as long as a
hydrogen/air mixture present in the main cylinder chamber is far removed
from being capable of igniting, whereas towards the end of the compression
stroke, when the hydrogen/air mixture in the main cylinder chamber 36 is
close to being ignitable, a lesser amount of hydrogen flows into this
chamber and, consequently, the hydrogen/air mixture in the main cylinder
chamber 36 will be kept below its ignitability more or less until the top
dead center is reached and this ignitability is not reached until more or
less immediately before the top dead center.
In addition, the second embodiment is also provided with a main injection
means 72 which opens directly into the main cylinder chamber 36 and serves
to inject hydrogen directly into the main cylinder chamber during the
suction stroke.
This second embodiment operates, in contrast to the first embodiment, such
that the major amount of hydrogen is injected via the main injection means
72 during the suction stroke so that a hydrogen/air mixture is already
formed in the main cylinder chamber 36, this major amount being determined
such that the mixture thus resulting is a weak mixture which has no or
only a negligible ignitability.
The remaining hydrogen is, as before, injected into the cylinder chamber 66
via the injector 64 and injected into the main cylinder chamber 36 via the
gap 68 during the course of the compression stroke so that the optimum
ignitable mixture again does not result until near the end of the
compression stroke. Thus, the same advantages can be achieved as with the
first embodiment.
The advantage of the second embodiment according to FIG. 4 is to be seen in
the fact that the auxiliary cylinder 42 and the auxiliary piston 44 can be
of a smaller construction and therefore the entire combustion engine can
be built in a more space-saving manner since a smaller amount of hydrogen
is injected into the cylinder chamber 66 and from there transferred to the
main cylinder chamber 36.
The present disclosure relates to the subject matter disclosed in German
application No. P 40 03 729.0 of Feb. 8, 1990, the entire specification of
which is incorporated herein by reference.
Top